Desulfurization of olefinic naphtha



April 7, 1953 R. c. ARNOLD ET AL DESULF'URIZATION OF' OLEFINIC NAPHTHA Filed NOV. 29, 1949 Patented Apr. 7, 17953 g UNITED srAi-as Meur r otr-rcet aesagso, y Y

Robert C. Arnold, Chicago Heights, Ill., and J ohn Deters; Valparaiso, Ind., assgnors. toStandr` ardjOil Company,l Chicago, IllaacorporationV of Indiana i Applieationmvember,29, 19.49-, Seriana. nasca rolf-time.` (o1. nui-24)A 1V y VThis.invention .relateskk to an improved method t to 400 F. An outstanding example of arliighsill-1l 015, desul'furizing ,highly l oleflnic naphthas yand it pertains more particularly to the desulfurization of coke. still naphtha `by extraction with dimethylsulfolanel containing lessthan715 per centof walsen the. .extract being hydrodesu-liurized for blending with therainate. Y i

Vdn obiectof the invention is to providefan improved method, and` means for removing Sulfur compounds lfrom highly oleiinic` naphthas, withoutmmaterially f altering the, olefin to paraiiin ratios. andA without sulieringj large treating losses A` particular objectk is tof desulfurize a naphthaA inwhichthe oleiinic` content substantially equalsv orexceedsV the parailinie content, an outstanding example of such lnaphtha being coke still naph-` tha. A furtherf object of the invention is to con.- verta high; sulfur olelnic naphtha into lowA sulfur olelnic gasoline of a high anti-knockvalue withI minimum treating losses and with. a minimum amount `of olens subjected to hydroning whenv that process is employed for vconvertingsulfur compounds to H25 for facilitating their removal from extract material.

Wehave discovered'that when 2xt-dimethylsulfolaneis employed for extracting a highly olenic naphthag'such` as coke still.v naphtha, the solvent does-not effect separation` betweenolens-'andfparafiins (as would be expected from U., S., 2,360,861), but.- on the contrary produces remarkably high raiiinate yields of substantially thefsame olefin to paraiiin ratio asthe initial charging Stock but with a remarkably def creasedv amount of sulfur and aromatic compo-y n ents..r` The selectivity of 2,4i-di-methylsulfolane for sulfur removal is unexpectedly much higherirrtheasel offsuch highly unsaturated low boil-- ing charging stock'than inthe case of satu-V rated charging y stocks or charging stocks ofl 1 higher boiling range. i i

`The accompanying drawing schematically illustratesa flow diagram of av system for practicing the invention.

The invention isapplicableto high sulfur ole. lnic naphthas generally, i. e, to naphthasv in which the oleiin to paraffin ratio is inthe range of;- about 3:1 toI 1:3 and is particularly advantageous for charging stocks in which the olefinie content exceeds the'paraiinic-content. By high sulfur, we mean a-sulfur content which is at, least about25 per cent and which1 is` usually in.

the-range of.v about*V .5to- 1 per cent or more. By naphtha we. mean a; normally liquid hydro.

` carbonffractionlboiling below 450. F. and. usually boiling;almostentirely within therange oi v100" fur olenic naphtha is the naphtha produced by the coking of high sulfurireduced crude in any known manner such, for example, as by contin-E uously introducingv heated charging stock intoa coke drum at about atmospheric pressure to '50 pounds per squarci inch at a temperature in the.-` range of about 850 toj950 EL, and continuing theY operation until coke solidies in the Adrum,I the vaporous products from. the drum being fracf tionated into a coke still naphtha fraction and one or more hea-vier fractions;v While the invenf tion may-be applicable tohigh sulfuroleii'nic-` naphthas*k producedy by thermal]V cracking o`rby i catalytic cracking, its outstanding; achfantage isfin the rening of cokel stillfna-phtha becauseY this'f'I particular high sulfur--olenic naphtha '-is'the* extract, respectively, can thus be employed to determine the extent tojwhi'chy olens are selec-f.v

tively removedjfromparains in an extractionI process.

Our extractant is 2,4'-dimethylsulfolane which, k boils at about 281" C. and which thusmaybe readily separated from ,naphtha raiiinatesxandV extracts by simple distillation.,` For optimum results, the dimethylsulfol'ane should contain a small amount of water which', should be less'than 10 per cent and usually in the range of, aboutito5 per centorapproximately 2per cent whenv the solvent to oil' ratio is ofthe order of 1*:1.;` with higher solvent to oil' ratios, the. waterV content maybe as high vas l5"per cent. The watery is most effectively utilized'when introducedjinto the extract portion of' a countercurrentextracf` tion system. Thus,1when a countercurrent tower; extractor is employed, a small' amount oi(V the water may be introduced with the solvent; at the top of the tower, but the water is most eiectively utilized when introducedinto the extract f y phase near thepont of charging stock, inletor between` this point and, the. bottorn` of ,the tower..

` i The; invention isA not t limited to,-.`,tower-; type, ei-

traction, however, and the extraction may be eected batchwise, in a multiple batch system, in a countercurrent batch system, or by any other extraction method known to those skilled in the art.

The extraction can best be carried out with a solvent to charging stock volume ratio in the range of .3:1 to 3:1, the preferred range being about .5:1 to 1:1. The extraction may be effected at ordinary room temperature or within the range of about C. to 40 C. Thepressure` should be such as to keep all material in liquid phase.

As a specific example of the invention, the following data were obtained when a coke still naphtha of about 80 bromine number containing .9 weight per cent sulfur wasextracted at room temperature with a 1:1 solvent ratio with 2,4- dimethylsulfolane having the indicated water content. These results were obtained in theV single batch extraction.

Percent Percent Percent Desulfuri- Prcn Wager Raiiinatc Sulfur in Desulfurization 1 n o veu Recovere Raiiinatc zation Selectivity 1 Percent desulfurlzation divided by treating loss.

Percent Percent Percent Desuliuri- Pgrcgm wat Ralnate Sulfur in Dcsulurization 1 m C' Vent Recovered Raffinatc zation cSelectivity 1 Percent desulfurization divided by treating loss.

It should be understood that increased concentrations of water may be used in either of the above examples in order to obtain higher ranate yields, but in so doing, somewhat lower desulfurization will result.

A surprising result is that the extraction of the high sulfur oleflnic naphtha does not produce any appreciable change in the paraiiin to olerln ratio. The charge in the countercurrent extraction example hereinabove set forth had a bromine number of about 80, the rafnate a bromine number of about 75, and the extract a bromine number of about 91. Since one weight per cent sulfur in organic sulfur products is equivalent to 5 bromine numbers, the bromine number of the feed may be broken down to a bromine absorption by olefins corresponding to about 75 and a bromine absorption due to sulfur corresponding to about 5. Since the ramnate contained .25 weight per cent sulfur, a like break down indicates a 74 bromine number for the olefin content thereof.

The extract, on the other hand, contained about 2.5 weight per cent sulfur so that the olen content thereof apparently had a bromine number of about '78. These data show that there is no appreciable separation of olei'lns from parafiins, i. e. no appreciable selectivity of 2,4-dimethylsulfolane for olenes when the solvent is employed for extracting a high sulfur olenic naphtha.

It should be pointed out that since the olenic naphtha, raffinate and extract are lower boiling than the solvent, separation of the solvent may be effected by simple distillation, although any final traces of solvent may be removed by water scrubbing if desired. An important feature of dimethylsulfolane in extracting high sulfur olenc naphtha is the fact that the solvent does not cause any condensation, polymerization or alkylation and does not combine with the olens (as is the case, for example, with hydrogen fluoride and certain other solvents) The sulfur contents of the rafinates produced by our invention are sufficiently low so that they may be blended in finished gasoline to meet stringent sulfur specifications. The extract which only constitutes a small fraction of the original charging stock, but which contains` most of the sulfur compounds, may be hydrodesulfurized by any known process, such, for example, as hydroforming, hydroning, autoning, etc. The catalysts employed for this step may be an eighth group metal or metal sulde as described in U. S.

2,273,297, but it is preferably a supported sixth'l group metal compound, such as chromium or molybdenum oxide on alumina as employed in hydroforming (note U. S. 2,388,536) or supported cobalt molybdate as used in hydroning (note Ind. Eng. Chem., vol. 35, pages 1160 to 1167), or tungsten nickel sulfide as described in the paper presented by Eagle and Rudy entitled Application of Cyclic Adsorption Process to Desulfurization of Cracked Naphtha before the American Chemical Society in September 1949. Autofining is similar to hydroning except that the hydrogen is supplied by naphthenes added to the charging stock. Since these hydrodesulfurization processes are Well known to those skilled in the art (product yields and product qualities, both alone and blended with initially separated components being likewise known, as described for example in the Eagle and Rudy paper), it is unnecessary to describe the hydrodesulfurization or the yields and properties of nished motor fuel in further detail.

An important feature of our invention is the remarkable effectiveness of dimethylsulfolane for removing from a high sulfur olefinic naphtha an extract which contains such a larger proportion of the original sulfur but so small a proportion of the original olens. Thus, if the per cent sulfur divided by the corrected bromine number of the high sulfur olenie naphtha, rafinate and extract respectively are compared, it will be found that this measure of sulfur to olefin ratio is 0.012 with the original high sulfur olefnic naphtha, 0.003 in the case of the raffinate and 0.03 in the case of the extract, the ratio in the case of the extract being ten times that in the case of the raffinate and about three times that in the case of original charge.y

Our invention provides an enormously simpler obtain a finished product blend of remarkably high octane number and at a relatively low cost. Since any water employed in our extraction 5 step is separated along with the raflinate and extract respectively while they are being distilled in the solvent recovery steps, the water may be separated from the distilled and condensed rainnate and extract respectively by simply settling condensed water from the oily layer and returning the settled water for example to an intermediate or low point in the extract tower. This provides a much simpler and less expensive operating procedure than processes wherein water distills with solvent from extractl and raffinate and cannot be separated from condensed solvent by simple settling.

Referring to the drawing, the high sulfur ole- `iinic naphtha charge `is introduced by line I to extraction tower II into which dimethylsulfolane is introduced through line I2 and a small amount of Water is introduced through line I3 and/or I4. Rafnate is introduced by line I5 to still I6 from which hydrocarbons and water are taken overhead through condenser I 'I to sep- Y arator-receiver I8, the oil from said receiver being withdrawn through line I9 for final blending, and the water being returned by line 20 to line I3 and/or I4. Extract is introduced by line 2| to still 22 from which oil and water vapors are condensed in cooler 23 and introduced into separator 24, separated water being returned by line 25 to line I3 and/or I4. Solvent is returned from still I6 by line 26 and from still 22 by line 21, said solvent being heat exchanged in exchangers 28 and 29, respectively, and then cooled incooler 30. Extract is withdrawn from settler 24 through line 3|, is hydrodesulfurized in sys- .for blending with raflinate from line I9 to give the final low sulfur, olenic gasoline.

While our invention has been described with respect to specific operating examples, it should be understood that alternative operating conditions and modifications will be apparent to those skilled in the art from the above description. Other alkyl sulfolanes, which are substantially equivalent in vextraction properties to 2,4- dimethylsulfolane, may be employed instead of 2,4-dimethylsulfolane itself.

We claim:

1. The method of obtaining a low sulfur olennic gasoline of high anti-knock value from a high sulfur oleiinic naphtha which comprises extracting a naphtha having an olen to paraln ratio in the range of 3:1 to 1:3 and containing more than .25 per cent sulfur with 2,4-dimethylsulfolane under conditions to form an extract phase containingA most of the sulfur and a rafnate phase containing most of the olens, employing with the 2,4-dimethylsulfolane in the extraction step an amount of water in the range of from about 1 to 5 percent by volume based on total solvent, separately removing solvent and Water from each of said phases, hydrodesulfurizing the solvent-free extract phase to eliminate sulfur therefrom and blending the hydrodesulfurized extract with the solvent-free raflinate to 6 2. The method of obtaining a low sulfur olefinic gasoline of high anti-knock value from a. high sulfur olenic naphtha which comprises extracting a naphtha having an olen to paraffin ratio in the range of 3:1 to 1:3 and containing more than .25 per cent sulfur with 2,4-dimethylsulfolane under conditions to form an extract phase containing most of the sulfur and a rainate phase containing most of the olens, employing with the 2,4-dimethylsulfolane in the extraction step an amount of water in the range of from about 1 to 5 per cent by volume based on total solvent, separately removing solvent from each of said phases by distillation under conditions to distill water with the raflinate and extract respectively, separately condensing distilled raflinate and extract along with any water contained therein to form condensates, settling water from at least one of said condensates and returning said separated water to the extracting step.

3. The method of claim 2 which includes the further steps of hydrodesulfurizing the solventfree extract to eliminate sulfur therefrom and blending the hydrodesulfurized extract with the solvent-free rainate. i

4. The method of converting a coke still naphtha having an olenic content greater than its paraiiinic content and having a sulfur content in the range of .25 to 4 percent into an olefinic gasoline of low sulfur content and 4high anti-knock value, which method comprises countercurrently contacting said coke still naphtha. with 2,4-dimethylsulfolane in an extraction zone, introducing an amount of water in the range oi.' about 1 to 5 percent by volume based on total 2,4-dimethylsulfolane into the extract end of said extraction zone, introducing an extract phase from the extraction zone to a rst distillation zone, distilling extract and Water from `2,4-dimethylsulfolane in the rst distillation zone, condensing vapors from said rst distillation zone and separating water condensate from the extract, recycling said water condensate to the extract end of said extraction zone, introducing rainate phase from said extraction zone to a second distillation zone, distilling raflinate from 2,4-dimethylsulfolane in said second distillation zone, returning undistilled 2,4-dimethylsulfolane from the base of both distillation zones to the raiiinate end of the extraction zone, hydrodesulfurizing the extract and blending the hydrodesulfurized extract with said raihnate to obtain said low sulfur olenc gasoline of high antiknock value.

ROBERT C. ARNOLD. JOHN F. DETERS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS.

Number Name Date 2,285,596 Dunn June 9, 1942 2,360,859 Evans et al Oct. 24, 1944 2,360,861 Pierotti et al, Oct. 24, 1944 

1. THE METHOD OF OBTAINING A LOW SULFUR OLEFINIC GASOLINE OF HIGH ANTI-KNOCK VALUE FROM A HIGH SULFUR OLEFINIC NAPHTHA WHICH COMPRISES EXTRACTING A NAPHTHA HAVING AN OLEFIN TO PARAFFIN RATIO IN THE RANGE OF 3:1 TO 1:3 AND CONTAINING MORE THAN .25 PER CENT SULFUR WITH 2,4-DIMETHYLSULFOLANE UNDER CONDITIONS TO FORM AN EXTRACT PHASE CONTAINING MOST OF THE SULFUR AND A RAFFINATE PHASE CONTAINING MOST OF THE OLEFINS, EMPLOYING WITH THE 2,4-DIMETHYLSULFOLANE IN THE EXTRACTION STEP AN AMOUNT OF WATER IN THE RANGE OF FROM ABOUT 1 TO 5 PERCENT BY VOLUME BASED ON TOTAL SOLVENT, SEPARATELY REMOVING SOLVENT AND WATER FROM EACH OF SAID PHASES, HYDRODESULFURIZING THE SOLVENT-FREE EXTRACT PHASE TO ELIMINATE SULFUR THEREFROM AND BLENDING THE HYDRODESULFURIZED EXTRACT WITH THE SOLVENT-FREE RAFFINATE TO FORM AN OLEFINIC LOW SULFUR GASOLINE OF HIGH ANTIKNOCK VALUE. 